WHO recommends new malaria bed nets to fight resistant parasites

The World Health Organization is recommending the use of malaria bed nets treated with new insecticides in areas with parasite resistance. Insecticide-treated bed nets are key tools for malaria prevention. Since 2005, over 2 billion of them have been distributed globally. But they have all been treated with one insecticide, pyrethroid. Mosquito resistance to this insecticide in a number of areas now poses a threat to malaria control efforts. The new recommendations combine pyrethroid with an additional chemical to overcome any resistance. The nets include a combination of pyrethroid and insect growth regulator pyriproxyfen or pyrethroid and the insecticide chlorfenapyr — which is highly recommended in areas with pyrethroid resistance, given its expected “increased killing effect.” According to the London School of Hygiene & Tropical Medicine, whose researchers have spearheaded large scale trials of pyrethroid–chlorfenapyr-treated bed nets in Tanzania and Benin, chlorfenapyr “induces muscle cramps in mosquitoes,” stopping them from flying. This means they are glued to the spot, unable to feed or fend for themselves, leading to their death. Research on chlorfenapyr spanned over 15 years. The COVID-19 pandemic also impacted its trials, extending the time it took to complete them, Manfred Accrombessi, assistant professor of epidemiology at LSHTM and the trial manager in Benin, told Devex. Both trials have shown significant reductions in malaria infections compared to the standard pyrethroid bed nets. In the Tanzania trial, malaria prevalence was lower in children that received the pyrethroid-chlorfenapyr-treated bed nets: 25.6% compared to 45.8% in those that received pyrethroid-only bed nets, after 24 months. The findings were similar in the Benin trial. After 18 months, malaria prevalence was only at 27.9% in the group that received the pyrethroid-chlorfenapyr-treated bed nets versus 38.7% in the group that received pyrethroid-only bed nets. According to LSHTM, findings from the trials mark “the first time a safe and effective new insecticide for use on nets has been demonstrated for 40 years.” What’s next Following the WHO recommendations, researchers anticipate the rollout of the new bed nets in malaria-endemic areas. In Benin, Accrombessi said that could happen as early as within the next two months. But he’s also conscious of the challenges in the uptake of new bed nets in communities. One of the things they’ve observed during the trial in Benin was families did not immediately use the new nets they received, and continued to use their old nets until they needed replacing. “We made a net coverage usage survey one month after the distribution, and it was around 52% of the community using the new nets,” Accrombessi said, leading them to conduct follow-up campaigns to ensure households used the new ones. Accrombessi said they’re thinking about the feasibility of giving a household more than one net to increase uptake, and to take out the old ones in return. This is for households with families whose members don’t all sleep in one room. But they still need to assess the feasibility of that. Pyrethroid-chlorfenapyr-treated nets cost $3.02 to procure, slightly higher than pyrethroid-only bed nets which cost $2.07. But researchers said the cost could be offset by savings from reduced malaria cases. Accrombessi said the focus should now be on developing a comprehensive long-term resistance management plan to ensure the long-term impact of the new nets — something that was missing when pyrethroid-only bed nets were rolled out.